The present invention relates generally to eddy current proximity systems and, in particular, to methods and systems used to facilitate reducing target material variation effects on digital eddy current proximity systems.
At least some known eddy current proximity systems may experience gap output signal variations that are relative to variations within a target material rather than variations of the actual gap distance. Specifically, variations in the target material properties may affect the proximity system output similar to a variation in gap distance. Such target material properties may be the result of mechanical or electrical runout, material anomalies, variations in material permeability, variations in material resistivity, plated surfaces, target surface damage, and/or magnetization. Specifically, in rotary targets, runout may be periodic in nature and may have a once-per-revolution content such that the proximity system may interpret such runout as shaft motion and vectorially add the total runout to the true target motion.
Runout may be generally defined as a mechanical imperfection in rotary machine shafts. Runout may also describe an output signal of a vibration pick-up that does not represent shaft vibratory motion, but rather is caused by the eccentricity of the shaft, by surface irregularities, and by properties of the shaft material that cause the vibration probe or transducer to give an incorrect vibration signal.
Proper finishing of the target surface may facilitate reducing mechanical runout, and/or shaft-peening and burnishing may facilitate reducing electrical runout. However, the aforementioned techniques have historically only been partially successful. Accordingly, within at least some known digital eddy current proximity systems, a known method that has been employed to attempt to remove or cancel the effects of variations in the target material properties by deriving an electrical signal that corresponds to the runout and then subtracting this runout signal from the vibration signal. However, such methods and systems may not be able to determine a correction signal in real-time that is adequate to significantly reduce the effects of the target material variation reliably.